[mythtv-users] Way out idea on watching same thing in multiplerooms

[Daniel Kristjansson]

On Mon, 2010-01-04 at 19:26 -0600, Greg Oliver wrote:
> Without broadcast quality hardware, there will be no synchronization..
>  Period..  And even then, certain architectures must be met..  You
> cannot have motherboard-x, videocard-y, nic-z and expect to accomplish
> *exactly* synchronized video...

This is simply not true. You need is a A/V player that will respect
a presentation time stamp and can adjust for the latency of an audio
system* and you need to measure the latencies of your audio system.
MythTV already requires ntp for time synchronization, that with that
and this non-existent A/V player and known audio delay you can
synchronize audio within a couple ms and video within one frame
delay (max 40 ms). The audio is actually more important, since it
carries between rooms.

Remember when you wired up your 5.1 speakers and there were all those
stern warning about getting the polarity right on each speaker? Well
being just half a wavelength off causes all kinds of havoc. Worst of
all is being between 50ms to 500ms off, it causes you to lose track
of what people are saying. It's like when you are speaking at a podium
and you can hear yourself echoing from the back of the hall, or when
the echo cancellation on a phone line is not working. You start to
speak and what you hear isn't what your brain expects, so unless you
train for it, you will stammer. Well it's not as bad when you're not
speaking, but it can still be mighty annoying.

Networking latency is irrelevant to synchronization.

-- Daniel

*I'm considering doing an overhaul of the MythTV video decoder later
this year, and Mark K has talked about working on the A/V Sync code.
But neither of us has actually done either so far, but it isn't beyond
the realm of possibility that this will get done this year. That alone
won't give sync, but it would allow one to play fully synced A/V in
multiple locations without too much extra work.